Vol. 8, No. 12, December 1969
MONOSUBSTITUTED HYDROXYACETYLENES 2591 CONTRIBUTION FROM THE RICHARDSON CHEMISTRY LABORATORIES, TULANE UNIVERSITY, XEW ORLEANS, LOUISIANA 70118
Platinum-Acetylene Complexes. 11. Monosubstituted Hydroxyacetylenes112 BY JOHK H . NELSON, H. B. JONASSEN,
AND
D. M . ROUNDHILL
Receioed M a y 1, 1969 The reactions of some whydroxyacetylenes with the complexes tetrakis(triphenylphosphine)platinum(O), I, and cis-dichlorobis(triphenylphosphine)platinum(II), 11, have been studied. Reaction of either I or I1 under appropriate conditions with 1-ethynylcyclopentanol, 1-ethynylcyclohexanol, 1-ethynylcycloheptanol, 3-methyl-1-butyn-3-01, l,l-diphenyl-2-propyn1-01, and 3-methyl-1-pentyn-3-01 yielded complexes containing M-bonded acetylenes. The C=C stretching frequency of the complexed acetylene in the infrared spectrum is lowered by about 400 cm-l over t h a t of the free acetylene and the acetylenic proton appears in the nmr spectrum as an AA’MX type of multiplet centered at 7 ~ 3 . ppm. 7 Mechanistic implications are presented and discussed.
Introduction A considerable number of mononuclear complexes of transition metals in low- or zero-oxidation states and various acetylenes have been reported. 3-5 Very often several products have resulted from these reactions ; among them were binuclear and polynuclear complexes as well as acetylene polymerization products. Very little attention has been given to the influence of steric and electronic effects of the acetylenes on the nature of the mononuclear products of platinum(1V)-, platinum(11)-, and platinum(0)-acetylene complexes, which have been known for some time.3-10 Only one study of electronic effectss concerning platinum acetylene cornplexes has appeared in the literature. Chatt, et aZ.,’ prepared platinum(I1) complexes of dihydroxyacetylenes and found that the hydroxy groups as well as the acetylene participated in bonding. The isolation of bisacetylide c o m p l e x e ~ led ~ ~ ’to ~ the decision to undertake a systematic study of the steric and electronic influences of the acetylenes on the structure of platinum-acetylene complexes. The first part of this study using a series of monosubstituted hydroxyacetylenes is reported herein. Experimental Section A. Reagents and Physical Measurements.-3-Methyl-lbutyn-3-01 (Aldrich), 1-ethynylcyclohexanol (Matheson Coleman and Bell), I-ethynylcyclopentanol (Farchan Research Laboratories), and 3-methyl-1-pentyn-3-01 (K & K Laboratories) were used without further purification. 1-Efhynylcycloheptanol (1) P a r t I : D. M. Roundhill and H. B. Jonassen, Chem. Commun., 1233 (1968). ( 2 ) Presented in part a t the 157th National Meeting of the American Chemical Society, Minneapolis, Minn., 1969; see Abstracts, No. INOR 103. (3) I. Wender and P. Pino, “Organic Synthesis via Metal Carbonyls,” Interscience Publishers, New York, N. Y., 1968, and references contained therein. (4) J. P. Candlin, K. A. Taylor, and D. T. Thompson, “Reactions of Transition Metal Complexes,” American Elsevier, New York, N. Y., 1968, and references contained therein. (5) R. Ugo, Coord. Chem. Re%, 3, 319 (1968), and references contained therein. (6) E. 0. Greaves, C. J. Lock, and P. M. Maitlis, Can. J . Chem., 46, 3879 (1968). (7) J. C h a t t , R. G. Guy, L. A. Duncanson, and D. T. Thompson, J . Chem. Soc., 5170 (1963). (8) J. Chatt, G. A. Rowe, and A. A. Williams, Puoc. Chem. Sac., 208 (1957). (9) A. D. Allen and C. D. Cook, Cas. J . Chem., 42, 1063 (1964). (10) M. I. Bruce, D. A. Harbourne, F. Waugh, and F. G. A. Stone, J . Chem. Soc., A , 356 (1968).
was prepared from cycloheptanone by the method of Dominguez and Garza.” l,l-Diphenyl-2-propyn-l-o1was prepared from benzophenone and lithium acetylide ethylenediamine (Foote Chemical) by the method of Beumel and Harris.lz All solvents were purified and freed from water by standard procedures and stored over Linde 3A molecular sieves for at least 2 days prior t o use. Tetrakis(triphenylphosphine)platinum(0Y3 and cis-dichlorobis(triphenylphosphine)platin~m(II)~~ were prepared according to literature procedures. Infrared spectra were recorded on a Beckman IR-8 infrared spectrometer as KBr pellets for the complexes and as neat liquids for the acetylenes. Proton nmr spectra were obtained on the Varian Associates Model A-60 as deuteriochloroform solutions with tetramethylsilane as internal standard. Melting points were determined in the air and are uncorrected. Elemental analyses were performed either by Alfred Bernhardt Laboratorium, Miilheim, Germany, or Galbraith Laboratories, Knoxville, Tenn. They are listed in Table I. B. Preparation of the Complexes. 1. LEthynylcyclohexanolbis(triphenylphosphine)platinum(O).-The two following methods were used to prepare this pbonded acetylene complex. Method 1.-To 0.60 g of ((C8Hs)sP)rPt suspended in 30 ml of nitrogen-degassed anhydrous ether was added 5 ml of l-ethynylcyclohexanol (nitrogen degassed). T h e flask was stoppered and stirred magnetically under nitrogen. After 3 h r a colorless precipitate formed, which was filtered, washed with 20 ml of anhydrous ether, and dried under vacuum over P,Olo. T h e yield was 0.320 g (79%) of colorless crystals, mp 142-143’ dec. Method 11.-To a suspension of 0.3010 g of cis-Cl*Pt((CGH&P)2 in 3 ml of absolute ethanol was added anhydrous hydrazine (97+ %, M C B ) dropwise until dissolution was nearly complete. (At the point of complete solution an unreactive yellow compound will precipitate. The nature of this yellow compound is not certain but is thought t o be an immine-bridged platinum dimer.15) The solution was then quickly filtered by suction and 3 ml of 1ethynylcyclohexanol was added. This sbhtion was heated just to reflux and allowed to cool slowly while being stirred magnetically for 2-3 hr. T h e resultant colorless microcrystalline precipitate (0.1000 g, 33.47,) was filtered, washed with 10 ml of absolute ethanol and 10 ml of anhydrous ether, and dried for several hours under reduced pressure over P ~ O I O ;mp 142143” dec. These complexes were recrystallized by solution in a minimum of cold nitrogen-degassed anhydrous benzene. T o this solution was added a n equal volume of anhydrous methanol and the benzene was evaporated without heating under a stream of nitrogen to incipient precipitation. (11) J. A. Dominguez and M. R. Garza, Ciencia (Mex.), PO, 134 (1960); Chem. Abslu., 66, 18627d (1961). (12) 0. F. Beumel, Jr., and R. F. Harris, J . Org. Chem., 29, 1872 (1964). (13) L. Malatesta and C. Cariello, J . Cham. Soc., 2323 (1958). (14) J. C. Bailar, Jr., and H. Itatani, Inoug. Chem., 4, 1618 (1965). (15) G. C. Dobinson, R. Mason, G. B. Robertson, R. Ugo, F. Conti, B. Morelli, S. Cenini, and F. Bonati, Chem. Commun., 739 (1967).
2302
JOIIN
H . NELSOK:,H. B.
JONASSEN, AND
Inorganic Chemistry
D. 11.ROUNDFILL
TABLE I ELEMESTAL -\SALYSES A S D PHYSICAL PROPERTIES --- Yocarbon----Yo hydrugen---. Found
Calcd
Found
Calcd
Found
Prepn method
62.11
61.93
4.80
4.87
7.34
7.46
I aiid 11
6" 62
62.41
5.02
5.02
7.22
7.22
I and I1
63 , 50
63.81
.?.IO
3.16
7.12
7.35
I and I I
147-149
61.08
61.36
4.88
4.82
7.70
8.00
I and I1
144-147
61.10
61.56
5.01
4.86
7.68
7.84
I and I 1
178-180
66.10
66.35
3.56
4.50
6.67
6.87
1 and I I
249-252
64.53
64.46
5.73
5.65
6.40
6.34
I
142-143
(iCeH i , P ) , P t H W
---Yo phosphorus-,
Calcd
OH
OH (
C,H ),P) Pt HCECC'CH,'
I
CH
OH
I
(CH P PtHCSCCHCH
I
CH,
OH
(
H
I' i :
I ir=ccc H
(iC,H )PIP t H IC-C
a
I CY
-OH7 3
)
All complexes melted with decomposition.
Per cent platinum:
2 . trans-Dihydridobis(triphenylphosphine)bis~l-ethynylcyclohexanol)platinum(IV).l--To 0.60 g of tetrakis(tripheny1phosphine)platinum(O) suspended in 30 ml of nitrogen-degassed ether
was added 3 ml of 1-ethynylcyclohexanol under nitrogen. T h e flaqk was stoppered and allowed to stand for 4 days. T h e initially yellow suspension gradually dissolved to form a colorless s3lution with th: slow deposition of colorless crystals. Xfter 4 days the solution v,-as concentrated to half-volume by aspiration a t room temperature, filtered, washed with 10 nil of anhydrous ether, and dried under reduced pressure over P ~ O tIo~ yield 0.0815 g (17.5Yc)of cdorless crystals, dec p t 249-252'. 3 . ti.ans-Hydridochlorobis(triphenylphosphine)platinum(II).T o a solution of trans-dihydridobis(triphenylphosphine)bis(lethynylcyclohexanol)platinutn(I~)(prepared as above) in ether was added 5 mi of carbon tetrachloride and the solution was stirred for 2 days. h colorless precipitate formed which was filtered, washed with ether, and dried under reduced pressure over PrOio; dec p t 200-2005', lit.'* value 210-215'. And. Calcd for C36H31C1P2Pt:C, 57.03; H , 4.09; P, 8.44; C1, 4.68; Pt, 25.74. Found: C , 56.85; H , 4.14; P, 8.59; C1, 4.97; P t , 26.50. 4. Tripropynylhydrazine Hydrobromide.-cis-Dichlorobis(triphenylphosphine)platinum(II) was suspended in ethanol and anhydrous hydrazine was added dropwise until solution was nearly complete and the solutim was filtered. To the filtrate was added 3-bromopropyne (Xldrich) dropwise. There was a n immediate exothermic reaction with gas evolution. T h e reaction mixture was stirred for 1 hr and the white crystals which formed were filtered, washed with ethanol, and dried under vacuum over P4010; m p 88-90". Anal. Calcd for NpHhBr: N, 24.8; H, 4.43; Br, 70.8. Found: C, 0.47; S,24.48; H , 4.57; Br, 70.18. T h e nmr spectrum possesses only one peak and thc infrared spectrum is very similar t3 t h a t of hydrazine dihydrochloride. T h e filtrate from the above reaction was heated just to boiling and stirred for 24 hr. A yellow solution formed and after 45 hr large white crystals precipitated. These were filtered, washed with ethanol and ether, and dried under reduced pressure over P4010; rnp 149-152 '. Anal. Calcd for tripr3~ynS-lhyiirazine
calcd, 24,35; found, 24.57 hydrobromide, CoHilSaBr: C, 47.6; H , 4.84; S,12.3; Br, 35.2. Found: C,46.99; H , 4 . 7 6 ; X, 12.14; Br,34.43. Hydrazine and 3-bromopropyne were also allowed to react i n the a.bsence of platinum under conditions otherwise identical with those above but hydrazine hydrobromide was the only crystalline product isolated.
Results The elemental analyses (Table I ) , infrared spectral data (Table II)! and pmr data (Table 111) indicate that the reactions of either tetrakis(tripheny1phosphine)platinum(O) or cis-dichlorobis(tripheny1phosphine)platinum(11) with hydroxyacetylenes yield stable platinum complexes having the stoichiometry [Pt( (CaH5)3P)2(HC2R) ] (type A). However, l-ethynylcyclohexanol also reacts with tetrakis(tripheny1phosphine)platinurn(O) to yield a complex B with the [ P t ( ( CaHi)3P)2 (HC2R)2 ] stoichiometry.
A
B
The infrared spectra of type A complexes do not shoTy a band in the region of VC-c but show a new band around 1880 cm-l (Table 11) attributable to VC=C, indicating that the carbon-carbon triple bond has been reduced essentially t o a double bond. The magnitude
Vol. 8 , No. 12, December 1969
MONOSUDSTITUTED HYI)ROXYACETYI,ENES 2593
TABLE I1 INFRARED SPECTRAL DATAFOR ---voa, Free ligand
Complex
THE
COMPLEXES
crn-I---.
Cornplex
r - v c E c , cm-1Free Complex ligand
OH
((C
H j P) Pt HC=C
a
3620
3570
2114
1681
3620
357n
2117
1686
3620
3.575
2120
1681
3440
3180
2120
16R8
A-
I 30
I
40
,, . L --L, 80 90
PPM (7)
Figure 1.-The 60-Mz spectrum of a typical type A complex in CDClr. T values are relative t o the TMS internal standard.
OH
I
( (C,H,) ,P)?P t . H C E C C CH,
I
3450
3390
2125
1670
3640
3400
2118
1678
8620
8620
2117
2120
~H,CH, OH
of the shift in U C - C is among the largest yet reported for acetylene complexes. The infrared spectrum of B showed a medium intensity peak a t 2120 cm-' which represents both VC=C and Vpt-H." This peak is however predominantly U P ~ - H as the complex prepared from deuterio-1 -ethynylcyclohexanol showed only a very weak peak a t 2120 cm-'. The 0-H stretching frequency, U O H , for type A complexes is shifted to lomer energy relative to that of the free acetylene by 45-260 cm-' while for type B complexes U O H remains unchanged. Some type of hydrogen bonding of the hydroxyl groups in type A complexes is thus indicated ; however, the OH resonance is found at higher field in the pmr spectra of type A and type B complexes than for the free acetylenes indicating less association of the hydroxyl group in the complexes , ~ that than in the free acetylenes. Chatt, et ~ l . found for platinum(I1)-dihydroxyacetylene complexes of the type K[PtClsRCzR], U O H shifted to lower energy by 110-140 cm-I and that the proton resonance of the , conhydroxyl proton shifted downfield by 1 . 5 ~both sistent with hydrogen-bond formation with the chlorine atoms OH---C1 upon coordination. Apparently platinum(0) interacting with the hydroxyl group causes a lowering in U D H while a t the same time it shields the hydroxyl proton. The pmr spectra of type A complexes have the following general features : an unresolved multiplet centered a t T 2.7 (phenyl), a singlet in the range T 8.3-9.2 (OH), and a multiplet consisting of at least four resolvable peaks centered a t T 3.7 ( C 5 2 - H ) . The C=C-H T value ( ? e ) P. W. Atkins, J . C. Green, and M . L. H. Green, J . Chem. Soc., A , 227.5 (1068).
in the vinyl region is consistent with the C=C absorption in the infrared spectrum indicating t h a t the coordinated acetylene is nearly equivalent to an alkene. A typical spectrum is shown in Figure 1. The C=C-H resonance may be interpreted as an AA'MX multiplet arising from coupling with platinum195 (nuclear spin I = I/%, 34y0natural abundance) and coupling with the two nonequivalent phosphorus-3 1 nuclei. Theoretically this would give rise to an apparent sextet with intensity ratios of 1: 5 : 6 : G : 5 : I . The experimental intensity ratios of the four resolved peaks are about 1: 1 : 1 : 1. The two outside members of the multiplet are not resolved. This may be because this resonance saturates very easily and these peaks are anticipated to be weak (only one-sixth of the most intense peaks). The coupl.ng constants obtained from the interpretation of these spectra are: 1 P t - H = 22 1 Hz, J p - - s 7 a n s . ~= 10 f 1 Hz, and J p - c i s - ~< 2 Hz. The AA'MX pattern has been previously observed for the methyl group in the compound" ((CGH6)sP)zPt. CHsCzCCsHb with J p t - ~ = 41.5 Hz, J p - - / 7 a n s . ~= 6.2 Hz, and J P - ~ ~ ~1-2 . HHz and for similar complexes of other methyl acetylenes.18 This pattern has also been observed by I9Fnmr for the CF3 group in the complex1g = 65.1 Hz ((C6H5)3P)2Pt . C F ~ C E C C F ~where J P B - F and J p - - F = 10.3 Hz. As pointed out by one of the referees the exact analyses of this coupling could best be determined by the use of a 100-MHz nmr spectrometer, which investigation is in progress with the cooperation of an investigator in another institution. The pmr spectrum of type B complexes shows three resonances. The two lower field ones consist of unresolved multiplets centered at T 2.39 (phenyl) and T 9.05 (CH2) with relative areas confirming the presence of one acetylene for each triphenylphosphine. The third resonance occurs a t T 22.88 and can only be due t o the hydridic hydrogen. The hydroxyl resonance is not resolved and must have shifted upfield from that of the free acetylene into
*
(17) E. 0. Greaves, R. Bruce, and P. M . Maitlis, Chem. Commun., 860 (1967). (18) J. H. Nelson and H. B. Jonassen, unpublished results. (19) J. L. Boston, S. 0 . Grim, and G. Wilkinson, J . Chpm. Sot., 3408 (1963).
H. 13. JONASSEN, 2591 JOHN H. NELSON,
TI.M.
AND
X M R SPECTRAL
I n orgil nic Chemistry
~M).
Vol. 8, No. 12, December 1969
MONOSUBSTITUTED HYDROXYACETYLENES 2595
Top view
Figure 3.-Proposed mechanism for reaction of ((CeH6)aP)t with acetylenes.
cis-ClzPt-
slight. ((C6H5)3P)3Pt, which has been shown by X-ray structure determination to have the trigonalplanar structure,21can be assumed to be the reactive species. It is a coordinatively unsaturated complex and can react readily with an acetylene (step 2 ) . For a bulky acetylene trans labilization of (C6H5)sP occurs (before rotation of the acetylene followed by cis labilization) and the platinum(1V) acetylide hydride complex (B) is formed (step 3b) by addition of a second molecule of acetylene. Hydroxyacetylenes have been shown to be better trans directors than triphenylphosphine. 22 Hydride transfer could then proceed either simultaneously or subsequent to platinum-carbon bond formation. On the other hand, for a small unhindered acetylene, rotation and cis labilization occurs before trans labilization and the p-bonded acetylene complex (type A) is formed. All of the presently available data are consistent with this mechanism which is similar to that proposed for nickel-catalyzed oligomerization of acetyl e n e ~ . ~ ~ * ~ ~ Preparation method I1 yields the p-bonded acetylene complexes (type A) irrespective of the steric factors of the acetylene. Figure 3 illustrates a mechanism consistent with these results. It has been shown t h a t hydrazine reduction of cis-ClzPt( (C~HF,)~P)~ proceeds through several steps,15 one of which is the first illustrated in Figure 3. The hydrazine-bridged intermediate (C) loses nitrogen very readily, and upon further addition of hydrazine trans-Pt((CeHj)3P)aHcl is formed.l6 Prior to the precipitation of trans-Pt((C6H5)aP)2HC1, a yellow compound suspected to be the immine-bridged dimer (D) is formed.15 An X-ray structural determination of the compound thought to be C showed i t to be a mixture of C and D. This yellow compound (D?) does not react with hydroxyacetylenes (vide supra). The postulate of intermediate C is further supported by the observation t h a t 3-bromopropyne reacts with an ethanol solution of I1 and hydrazine to form hydrazine hydrobromide and tripropynylhydrazine hydrobromide.25 Hydrazine, however, reacts with 3-bromopropyne to form only hydra(21) V. Albano, P. L. Bellon, and V. Scatturin, Chem. Commun., 507 (1966). (22) T. P. Cheeseman, A. L. Odell, and H. A . Raethel, ibid., 1496 (1968). (23) L. S.Meriwether, F. G. Colthup, and G. W. Kennerly, J. Ovg. Chem., 26, 5155 (1961). (24) L. S. Meriwether, M. F. Leto, E. G. Colthup, and G. W. Kennerly, ibid., 27, 3930 (1962).
O P t
Side View Figure 4.-Orbitals
participating in bonding for metal-acetylene complexes.
H
I
N
N
I
H C
H
I
H D
zine hydrobromide under the same conditions. It is thus reasonable to assume t h a t C also is an intermediate in this reaction. Sinceit is not possible a t this time to distinguish between symmetrical and unsymmetrical cleavage of C, only the symmetrical mechanism, which the authors favor, is illustrated. (25) T h e identity of these two compounds was established by elemental analyses and infrared and nmr spectra. Pertinent d a t a for tripropynylhydrazine hydrobromide follow: infrared (KBr disk), YC.C a t 2120 cm-1 (strong); t h e nmr in DMSO-& with DSS internal reference showed five peaks-a quintet a t T 7.44 (DMSO-&), a broad singlet a t T 6.52 (Hz0 in DMSO), a doublet a t 7 5.29 (CHz, J = ZHz), a triplet a t T 5.84 (CSC-H, J = 2 Hz), and a broad singlet a t r 3.58 (NH). T h e integrated intensities wereintheratio5:3:2 for (CHz): (CSC-H): (NH).
Recently one-electron semiempirical molecular orbital calculations were performedZ6sz7on a series of platinum-acetylene and - olefin complexes in order to ascertain the mode of bonding and to explain the physical properties of the complexes. Calculations were performed for two configurations, planar and pseudotetrahedral. The calculations clearly illustrate t h a t the complexes are best represented by three-coordinate platinum(0) with dp2 hybridization in the planar case and d2p hybridization in the pseudotetrahedral case. A bonding scheme, derived with the aid of group theory, t h a t is consistent with the molecular orbital calculations is shown in Figure 4. Greaves, Lock, and Maitlis6 have come to the same conclusion about the bonding in acetylene complexes based upon molecular orbital arguments and they proposed that the complexes should best be represented by R
R
a formula which appears to be the least misleading. The calculations indicate that upon coordination the acetylenic hydrogen becomes negatively charged which is in accordance with the observation that reaction of I with acetylenes in the presence of methanol, ethanol, or water yields type A complexes whereas in the presence of acetic acid type B complexes are formed. The planar and pseudotetrahedral configurations were found to differ only slightly in energy. Thus the complexity of the C r C - H resonance in the pmr spectra might possibly be explained by the presence of both forms in solution.28 Further work along these lines is now in progress. Acknowledgment.-\Ye thank Dr. M. Gordon and Dr. L. C. Cusachs for their helpful and stimulating discussions concerning this work and blr. Gordon Boudreaux for obtaining the pmr spectra. The financial support of the Esso Research Laboratories, Humble Oil and Refining Co., Baton Rouge, La., is gratefully acknowledged. \\:e appreciate the assistance provided by the National Science Foundation through Chemistry Research Instrument Grants GP-1690, GP-3203, GP-6915, and GP-8237. (28) h - 0 ADDED ~ ~ in PRoof .-The acetylene in these complexes exchanges 6,15120 according t o t h e reaction
E
slowly
(26) J. H. Nelson, K. S. Wheelock, I-. C. Cusachs, and H. B. Jonassen,
C h e m . C o m i n u x , 1019(1969). (27) J. H. Nelson, K . S. Wheelock, I,. C. Cusachs, and H. B. Jonassen, J . A m . C h e m . Soc., in press.
P ~ [ ( C S H ; ) ~ P I ? ( R Ci ~H CDCla ) --+ Pt[(CsHj)3P]zCl(CDClz)
+ RCzH
as shown b y t h e slow appearance of peaks attributable t o free acetylene.
CONTRIBUTION FROM THE DEPARTMENT OF CHEMISTRY, EXORY USIVERSITY, ATLANTA. GEORGIA 3032.'
cis and Charge Effects in Platinum(I1)-Catalyzed Substitution Reactions of Platinum(1V) Complexes BY SUS-kK G. BAILEY
AND
RONALD C. JOHNSOX
Received M u y 8,1569
+
+
+
Reactions of the type trans-Pt(SH3)4C122+ 4- Pt(dien)AnC 2Br- .--f trans-Pt(dien)ABr%"+ Pt(SH3)4*+ ZC1- and Pt(dien)Br+ trnns-Pt(dien)AC127'+ 2Br- +. trans-Pt(dien)Br3+ Pt(dien)A"+ 2C1- (where A = XO,-, Br-, or NH3; n = 1 or 2 ; dien = diethylenetriamine) were found t o have third-order rate laws, with first-order rate dependences on the reactant Pt(1Y) complex, the reactant Pt(I1) complex, and bromide ion concentrations. T h e fastest reaction was less than ten times faster than t h e slowest, which indicates t h a t cis and charge effects are relatively minor. T h e relative rates parallel the ease of oxidation of Pt(dien)ArL+ and of reduction of trans-Pt(dien)AClZD+. T h e r a t e d a t a are interpreted in terms of a bridged inner-sphere redox mechanism involving an activated complex of the type Pt-C1-Pt. R a t e constants and activation parameters are reported. Equilibrium constants related t o these reactions were studied spectrophotometrically and correlated with t h e r a t e data.
+
+
Introduction Numerous papers have appeared in recent years concerning detailed aspects of substitution reactions of platinum(1V) cations. For these reactions, the (1) F. Basolo, M.L. Morris, and R. ti. Pearson, Discussioizs Pavaday Soc., 29, 80 (1960). ( 2 ) F. Basolo and R. G. Pearson, Adaaiz. Inoig. Chetn. Radiochem., 3, 35 (1961). (3) W. R. Mason, 111, and R. C. Johnson, l a o v g . Chem., 4, 1258 (1065). ( 4 ) R. C. Johnson and E. R. Berger, ibid., 4, 1262 (1965). ( 5 ) R . R . Rettew and R . C. Johnson, ibid., 4 , 1566 (1965).
+
+
observed first-order rate dependence on the concentrations of the platinum(1V) complex, the entering halide ion, and a platinum(I1) complex is consistent with a mechanism proposed by Basolo and Pearson2 involving an inner-sphere two-electron transfer followed by (6) Vi'. R . Mason, 111, E. R. Beraer, and R. C. Johnson, i b i d . , 6, 248 (1967). (7) R. C . Johnson and E. R. Berger, ibid.,I , 1666 (1968). (8) A . Peloso and G. L)olcetti, C o o i d . Cheni. Rev., 1, 100 (1066). (9) A . Peloso a n d G . Dolcetti, Gazz. Chim. I t a l . , 97, 120 (1967).
